Tutorial - CMYK subtractive synthesis.

Subtractive colour synthesis is a colour reproduction process in which certain colours are successively subtracted from the initial white colour. Subtractive synthesis is typically used in colour printing and in the traditional visual arts such as painting, watercolour, screen printing, etc, In these techniques, it is common to start with a white support (paper, canvas), which reflects all the colours. By successively applying translucent inks or paints, certain tints are eliminated to obtain the desired colour.

There are generally three colours used for subtraction: cyan, magenta and yellow (hence the acronym CMY). These three colours are known as the primary colours, since all the others are obtained from them. In printing, black ink is used in addition to the primary colours. This is known as CMYB. However, black plays little part in colour reproduction, even though it makes it easier to obtain dark colours. Black ink has been added for the following reasons:

• Without black ink, you would have to mix the three primary colours to obtain black, which would consume three times as much ink. When you consider that the printed pages of a book (without illustrations) contain only black, it's easy to see why this ink was added.
• A better result (a blacker black) is obtained with a single black ink rather than a mixture of three inks.

Note: some printers commonly use the same primary colours as video: red, green and blue.

CMY colour simulator.

To familiarise yourself with subtractive synthesis in CMY mode, play with the three sliders and observe the resulting colour.

Standard colours: Black - Red - Green - Blue - Yellow - Magenta - Cyan - White

The concept of colour space.

Colour synthesis is always carried out in a neutral (or theoretical) colour space, i.e. it is assumed that the colours are perfectly rendered by the device, which of course is not possible: all peripherals have inaccuracies in their colour reproduction. In the case of printing, you also have to take into account the fact that paper is never completely white. Theoretical spaces are nevertheless used by all graphics software for their internal calculations, with corrections related to the peripheral are applied just before printing.

The most common neutral colour spaces are sRGB, AdobeRGB, ProfotoRGB.
We invite you to consult our tutorial "Colorspaces".